1. Field of the Invention
The present invention relates to a bandwidth measuring method and device. In particular the present invention relates to a bandwidth measuring method and device which monitor a traffic trend and evaluate an impact to a flow quality (packet loss).
2. Description of the Related Art
In order to evaluate an impact to a flow quality of packets which flow over a network, not only a general (long-term) mean or average transition of an overall traffic but also a local (short-term) traffic change is required to be grasped. For grasping such a traffic trend, the following prior art methods have been well known:
(1) Continuous Packet Capturing Method
This is a method of continuously capturing all of the packets to grasp a traffic trend.
Advantage
Since all of the packets are captured, a local packet behavior which may have an impact on the flow quality can be grasped.
Problem
Since the packet capture depends on a memory and a processing load, there is a limit to a capacity and a time for allowing continuous capturing.
(2) Statistic Sampling (SFlow/NetFlow) Method: FIG. 15
This is a method, as shown in FIG. 15, of grasping a general packet behavior of a traffic by statistically performing thinned-out sampling (shown by hatched lines) to packets to be captured.
Advantage
It is possible to reduce a capturing load because all of the packets are not required to be captured, so that a general traffic trend can be grasped with a small memory.
Problem
A local packet behavior which may have an impact on the flow quality can not be grasped.
For the above-mentioned methods (1) and (2), there have been proposed methods (link available bandwidth management method and bandwidth expansion timing estimating method), as shown in FIG. 16, in which a link available state is measured per short time “t” by measuring a traffic with an external device or module different from a network device, and a bandwidth expansion timing is estimated by extracting the number of times when the traffic in a short section “t” exceeds a threshold in each link (transmission line) set (see e.g. patent document 1).
Also, there has been proposed a bandwidth monitoring device which has a threshold for starting a probabilistic violation determination, a tilt value for determining its discard probability, and a monitor counter, wherein all of the packets are determined to be a monitor bandwidth violation when an amount exceeds a certain threshold (see e.g. patent document 2).
[Patent document 1] Japanese patent application laid-open No. 2002-118557
[Patent document 2] Japanese patent application laid-open No. 2004-254164
In the patent document 1, the short time unit for measuring the traffic is practically determined within a range of a memory, failing to take account of an impact to an application such as an actual packet loss. Although data per short time is aggregated, this technology is based on the premise that all of the packets are captured, so that the capture load is still large.
The patent document 2 is also based on the premise that all of the packets are captured. This is a technology of determining the bandwidth violation of an individual traffic (local traffic) such as a burst traffic, but not a technology used for grasping a trend of an overall traffic behavior, so that the capture load is large.